Food industry and packaging industry

This contamination has to be removed or reduced here, too. This is executed in order to protect consumers and to ensure a safe and cost-efficient production process. The condition of the final product must remain unchanged during packing and filling of the products. Beverages and food in particular must be treated very gently, and no contamination may subsequently occur (directly or indirectly).

Direct contact: The compressed air comes directly into contact with the product or packaging material or gets into the respiratory system or onto inner or outer spots not protected by skin (e.g. following an injury).

Indirect contact: The compressed air is discharged to the ambient air during an application. The expanded compressed air only reaches an object over a corresponding distance and having been diluted by normal ambient air.

The primary potential risks are:

• Contamination of the product by contaminated water (condensate)

• Contamination of the product by liquid oil (compressor oil)

• Contamination of the product by oil vapour or general gaseous hydrocarbons and thus undesirable essences

• Contamination of the product by undesirable metallic or non-metallic solid particles from the compressed air system, e.g. rust, corrosion particles, abrasion, sealing material or other loosened deposits

• Contamination of the product by undesirable micro-organisms

Use Case Food & Beverage

Particles, oil-aerosol and vapour, materials containing silicone as well as condensate are the main causes of faults in the paint shop. The use of compressed air in painting technology makes requirements on the cleanness of the compressed air which even go beyond the classes defined in ISO 8573-1.

Paints and varnishes react extremely sensitively to certain contamination in the compressed air. This results in coating wetting problems in the form of craters and bubbles, linked to corresponding rework and thus additional expense. The compressed air must be paint compatible i.e. free of substances which interfere with coating wetting (these include graphite, waxes, metal soaps, paraffins, talcum, teflon and plastic abrasion).

Paint-compatible compressed air is required when the compressed air comes directly or indirectly into contact with still wet paints or varnishes or surfaces to be painted. Whereas indirect contact can be avoided by cabins, direct contact is unavoidable wherever painting nozzles are used.

For this reason, paint-compatible compressed air must always be

• dry,

• free of liquid contamination, oil and aerosols,

• free of vapour phases which may condense,

• free of dust and other solid particles down to tiniest residual amounts.

Like greases or oils, the silicones dreaded in painting technology can be present in different phases (solid, liquid, gaseous) in compressed air. Contamination containing silicone can be removed using appropriate filters. However, gaseous and thus volatile silicone compounds can only be removed from the compressed air by means of catalytic oxidation. For this reason, the use of at least one catalytic converter is essential for the production of paint-compatible compressed air.

Wherever there is direct contact during the processing of raw materials (powders and granules), the compressed air must be absolutely dry and oil-free. This is the only way contamination and the formation of agglomeration can be excluded. In order to guarantee process reliability, both permanent monitoring and complete documentation of the compressed air quality are indispensable.

Use Case

Chip manufacturing processes must take place under clean room conditions i.e. the quality of the compressed air must be adapted to these requirements.  Another field of application for compressed air is the application of solder paste on the circuit board as well as cleaning of circuit boards, electronic printed circuit boards and wafers. The compressed air utilised here must be free of particles, oil and moisture.

Uses Case

Powder coating, also known as powder painting, is a coating process that is suitable for metallic and non-metallic objects. On the one hand, powder coating enhances the value of the treated object. On the other hand it serves to protect the object. There are two processes - the electrostatic powder coating (EPS); and the whirl sintering method. Compressed air is used e.g. to convey the powder, for fluidization or as dosing air and is a decisive factor for the final quality of the product. This is because oily compressed air can lead to open spots (craters) in the paint coating or to bubbles or craters in the fluid reservoir.

Technically oil-free compressed air still contains hydrocarbons as well as various fragrances and essences which would lead to loss of quality and odour pollution. Smaller partial volumes can be treated with microfilters or activated carbon filters. Larger volumes are treated using activated-carbon adsorbers. A filter can only remove oil droplets from the compressed air, whereas an activated-carbon adsorber can also remove hydrocarbon vapours from the compressed air. An activated-carbon adsorber always has to have an upstream high-performance filter and dryer for preliminary filtering.

Activated carbon is also used to remove the vaporous residual oil. Cleaning of compressed air by adsorption is a purely physical process. Oil molecules are bound by the adhesive forces of the surface of the activated carbon and the compressed air thus cleaned. No chemical compound is formed. The quality of the activated carbon is not obvious, yet it is of decisive importance, because activated carbon does hard work. Differences only become apparent when the service life does not meet expectations. As large an inner surface and as fine a pore system in the activated carbon as possible are required to prevent the accumulation of undesirable pollutants.

The dried and filtered compressed air is routed by a diffuser into the loosely shaken up activated carbon bed. This enables long contact times and optimum utilisation of the adsorbent. At some point, the activated carbon is saturated and can no longer carry out cleaning. From this time onwards, the residual oil content of the compressed air increases again. In other words, activated carbon is a consumable that cannot be regenerated and has to be replaced after approx. 8000 to 10000 operating hours. If the filters are serviced regularly, only a small residual oil content remains in the compressed air, which complies with the requirements of compressed air classes 1-2 in accordance with ISO 8573-1.

An activated carbon adsorber must always be preceded by a high-performance filter and a dryer for pre-filtering to prevent contamination of the activated carbon with particles, water and aerosols. Since the compressed air sweeps along coal dust particles from the activated carbon bed, an oil-free dust filter should be installed downstream for safety reasons. If these conditions are met, an activated carbon adsorber protects your system from oil ingress and is also characterised by a low differential pressure and long filter standing times.

This is the direct way of avoiding additional contamination of compressed air by oil through the compressor. Compressed air is produced by oil-free piston or screw compressors without the compressed air coming into contact with liquid or vaporous oils because the compressor chamber is not lubricated and pairs of screws run without touching each other. Compressed air produced in this way is often described as being “technically oil-free”. This is only possible thanks to perfect sealing and maximum precision. This involves high investment costs and limited operating pressure.

Does an oil-free compressor offer complete safety?
It is true that use of an oil-free compressor leads to no additional oil getting into the compressed air system. Since contamination (such as exhaust gases from vehicle combustion engines or heating systems, oil aerosols and micro-organisms) is already contained in the intake air, however, and is present in concentrated form downstream of the compressor, the compressed air always has to be treated. The oil content is often ≥ 0.01 mg per cubic metre (Class 2 or an even poorer rating).

If you are not sure which technology is the right one for your application, please use our decision finder for oil-free compressed air. This will give you an initial tip / approach as to which solution you should rely on.